The present invention relates to a method for cleaning semiconductor products of particles attached to the surface of the said product, as well as of metallic, inorganic and organic contamination.
The production of semiconductors such as silicon wafers is normally started with essentially pure silicon material. This material is grown in a pyrometallurgical process into a bar-like single silicon crystal, which is further cut to thin disk-like slices. Two important criteria for silicon wafers, used for instance in circuit building in the electronic industry, are extreme smoothness and purity. Even slight levels of impurities, as well as small irregularities of surface, make the obtained semiconductor product unfit for use. In order to remove impurities from the surface of the semiconductor product, the product is cleaned at various stages of the production process.
The purpose of washing the semiconductor product is to remove impurity particles accumulated on the surface of the wafer, as well as metallic and organic contaminations. Alkaline hydrogen peroxide solutions, the most popular among which is ammonia-hydrogen peroxide-water solution, are very efficient in removing impurity particles from the surface of a semiconductor product. In generally used ammonia-hydrogen peroxide-water solutions, the dilution ratio is for instance 1:1:5, which means that the solution contains one part ammonia and one part hydrogen peroxide per five parts water. However, the operating temperature of this kind of washing solution is about 70.degree. C., which means that the solution must be separately heated in order to make it ready for use. In this type of alkaline solution, some metals--for example iron, zinc and aluminium--tend to accumulate on the surface of the semiconductor product during the washing stage. For removing the said metals, there are generally used hydrochloric acid-hydrogen peroxide-water solutions, but after a washing with these solutions, the surface of the semiconductor product easily attracts particles. Another suggestion is to use weak ammonia-hydrogen peroxide-water solutions, but also after washing with these solutions, metals tend to remain on the surface of the semiconductor product.